Oxidations with Other Reagents

Selenium dioxide can be used to oxidize ketones and aldehydes to a-dicarbonyl compounds. The reaction often gives high yields of products when there is a single type of CH2 group adjacent to the carbonyl group. In unsymmetrical ketones, oxidation usually occurs at the CH2 that is most readily enolized.255 

The oxidation is regarded as taking place by an electrophilic attack of selenium dioxide (or selenous acid, H2Se03, the hydrate) on the enol of the ketone or aldehyde. This is followed by hydrolytic elimination of the selenium.258 

Methyl ketones are degraded to the next lower carboxylic acid by reaction with hypochlorite or hypobromite ions. The initial step in these reactions involves base-catalyzed halogenation. The a-haloketones are more reactive than their precursors, and rapid halogenation to the trihalo compound results. Trihalomethyl ketones are susceptible to alkaline cleavage because of the inductive stabilization provided by the halogen atoms. 

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Ruthenium tetroxide readily converts secondary alcohols to the corresponding ketone, and primary alcohols to aldehydes and acids.288,294 It is particularly recommended for converting alcohols which are difficult to oxidize with other reagents, for example, the hydroxylactone (105a) in equation (112).325... 

Again, as with pyridopyrimidines, the main reaction is oxidation of di- or poly-hydro derivatives to fully aromatic structures, often merely by air or oxygen. In some cases the reagent of choice is mercury(II) oxide, whilst other reagents used include sulfur, bromine, chloranil, chromium trioxide-acetic acid, hydrogen peroxide, and potassium ferricyanide, which also caused oxidative removal of a benzyl group in the transformation (306) (307)... 

The sisyl ether is stable to Grignard and Wittig reagents, oxidation with Jones reagent, KF/18-crown-6, CsF, and strongly acidic conditions (TsOH, HCl) that cleave most other silyl groups. It is not stable to alkyllithiums or LiAlH4. 

Note This is a useful reagent, at least for the oxidation of 2-chloroquinoxahnes. With other reagents such substrates usually give only their 4-oxides, but with this reagent they appear to give exclusively their 1-oxides. 2-Butyl-3-chloroquinoxaline (245, R = Bu) gave 2-butyl-3-chloroquinoxaline 4-... 

Primary and secondary aliphatic nitro compounds have been oxidized to aldehydes and ketones, respectively (RR CHN02 RR C=0) with sodium chlorite under phase-transfer conditions, TPAP, Oxone , as well as with other reagents. 

Whereas the original Moffat-Pfitzner oxidation employs dicyclohexylcarbodiimide to convert DMSO into the reactive intermediate DMSO species 1297, which oxidizes primary or secondary alcohols via 1298 and 1299 to the carbonyl compounds and dicyclohexylurea [78-80], subsequent versions of the Moffat-Pfitzner oxidation used other reagents such as S03/pyridine [80a, 83] or oxalyl chloride [81-83] to avoid the formation of dicyclohexylurea, which is often difficult to remove. The so-called Swern oxidation, a version of the Moffat-Pfitzner oxidation employing DMSO/oxalyl chloride at -60°C in CH2CI2 and generating Me2SCl2 1277 with formation of CO/CO2, has become a standard reaction in preparative organic chemistry (Scheme 8.31). 

The technique is versatile for determination of a wide variety of species that can participate in the CL process, such as CL substrates or CL precursors responsible for the excited state the necessary reagent for the CL reaction (usually an oxidant) some species that affect the rate or efficiency of the CL reaction activators such as catalysts (enzymes or metal ions) or inhibitors such as reductants that inhibit the CL emission fluorophores in the case of sensitized CL some species that are not directly involved in the CL reaction but that can react with other reagents in coupled reactions to generate a product that is a reactant in the CL reaction species that can be derivatized with some CL precursors or fluorophores, being determined by direct or sensitized CL. 

In contrast with other reagents, selective oxidation of methylcyclohexenes can also be achieved. 

Acetoxylation. Transformations of Carbonyl Compounds. Phenolic Oxidation. Oxidation of Nitrogen Compounds. Hypervalent iodine Reagents in Combination with Azido Compounds. DIB and Sodium Azide in Combination with Other Reagents. Transformations of Alkynes Involving Thiophenols and Diphenyl Diselenide. Miscellaneous Reactions. 

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